1. Field of the Invention
This invention relates generally to a tone quality control apparatus, and specifically to a digital tone control apparatus using digital signal processing. This invention also relates to a method of controlling tone quality.
2. Description of the Prior Art
Recently, digital signal processing technics have remarkably entered the field of sound. Especially in the field of hall sound, finer sound making or generation has been performed by development of digital mixers, digital equalizers, or other digital devices.
Some speaker systems have their own channel dividers and perform primitive unit correction in addition to the channel division. Such techniques have also advanced sound control in hall sound systems.
In some conventional hall sound systems, audio or musical signals inputted via microphones are mixed and converted by a mixer into a mixed sound signal, which is fed to an equalizer. The equalizer performs filtering of the sound signal at an adjustable frequency characteristic. This filter characteristic is generally adjusted in accordance with a frequency characteristic of a hall and a frequency characteristic of a sound reproducing speaker system. An output sound signal from the equalizer is applied to a channel divider. The channel divider separates the inputted sound signal into plural bands and thus derives plural sound signals corresponding to the respective bands. The channel divider generally includes analog filters for the band division. The band-divided sound signals are fed to power amplifiers respectively. After amplification by the power amplifiers, these sound signals are inputted into respective units of the speaker system, such as a tweeter, a mid-range, and a woofer. The units of the speaker system convert the respective sound signals into corresponding sounds.
In these conventional sound systems, adjustment of the filter characteristic of the equalizer and adjustment of characteristics of the filters in the channel divider allow a frequency characteristic of sound reproduction to vary. Since the filters in the channel divider are of the analog type and also the equalizer is of the analog type, this allowable variation in the frequency characteristic is generally broad and gentle and, usually, frequency characteristics of the respective bands can not be varied independently even when the equalizer has a 1/3 octave band-width. Therefore, it is generally difficult to flat or compensate sharp peaks and dips in the original sound pressure frequency characteristics of the respective units of the speaker system. It should be noted that such peaks and dips in the frequency characteristic cause a problem in aural sensation.
Advanced hall sound systems use an accurate digital equalizer. Usually, it takes a long time to set or adjust the digital equalizer to optimize the frequency characteristic.